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Exploring AAA and TACAS Configuration with Cisco Modeling Labs

October 29, 2024
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I’ll admit to not having achieved an intensive verification. Nonetheless, I’d nonetheless wager cash that AAA/RBAC providers are extra ceaselessly talked about on Cisco certification blueprints than another networking matter. From the CCNA to the Skilled degree, you’ll discover AAA, TACACS+, RADIUS, and RBAC listed on the examination subjects.

Here’s a handful of examples if you happen to’d prefer to test it out your self:

  • 200-301 CCNA
    • 2.8 Describe AP and WLC administration entry connections (Telnet, SSH, HTTP, HTTPS, console, and TACACS+/RADIUS)
    • 5.8 Differentiate authentication, authorization, and accounting ideas
  • 350-401 ENCOR
    • 5.1 Configure and confirm machine entry management
  • 300-410 ENARSI
    • 3.1 Troubleshoot machine safety utilizing IOS AAA (TACACS+, RADIUS, native database)
  • 300-430 ENWLSI
    • 8.1 Implement machine entry controls (together with RADIUS and TACACS+)
  • 350-701 SCOR
    • 2.7 Configure AAA for machine and community entry equivalent to TACACS+ and RADIUS
  • 300-715 SISE
    • 7.0 Community Entry Machine Administration
  • 350-601 DCCOR
    • 5.xa Apply community|compute|storage safety – AAA and RBAC
  • 300-615 DCIT
    • 5.xb Troubleshooting community|compute|storage safety – AAA and RBAC
  • 350-501 SPCOR
    • 1.6b Describe administration airplane safety – AAA and TACACS
  • 300-540 SPCNI
    • 4.1e Implement infrastructure safety – TACACS

OMG. That’s 10 totally different certifications from Affiliate to Skilled the place these subjects present up. You’ll additionally discover them on Skilled-level exams, such because the Enterprise Infrastructure, Enterprise Wi-fi, Safety, Service Supplier, and Knowledge Heart labs. (If anybody on the market can discover one other matter with as broad a protection, please let me know within the feedback. I’d like to know what I’ve missed thus far.)

Go to the Cisco Studying Community to view the examination subjects for all Cisco certification exams. View examination subjects

Okay… it’s positively vital… however what is AAA?

AAA is a crucial matter, but it surely’s one which even long-time community engineers could not totally perceive. So earlier than we see it in motion, how a couple of fast overview of what the “triple A’s” imply?

Carl sees how Authentication, Authorization, and Accounting are separate and vital steps for machine administration.

Within the “AAA in Motion!” comedian, Carl experiences all the AAA course of:

  • The primary “A” stands for Authentication. We see this represented when Carl is prompted to confirm his id earlier than he’s allowed to make a change to the community.
  • The second “A” stands for Authorization. Even after the community verifies Carl’s id, he has to examine whether or not he has the suitable(s) to make this alteration, based mostly on which rights he has been granted on the community.
  • And the third and last “A” stands for Accounting, which Carl sees in motion when the community logs the change he makes to the community.

TACACS comes into the image to help the centralized administration of customers, roles, and logs (authentication, authorization, and accounting). Whereas every community machine could possibly be regionally configured to deal with AAA, this doesn’t scale effectively for enterprises. A greater answer is for every community machine to speak with a central “server” for these actions. TACACS is a protocol that community units and servers use to speak and deal with every of the “A’s.” A “TACACS Server” is a software program utility that helps the TACACS protocol.

Can we get to the Exploration, already?!

Now that we perceive the essential position that AAA performs in a community (and that it’s a vital matter throughout many certifications), I’d like to indicate you tips on how to research and put together for it utilizing my favourite community simulation/virtualization device: Cisco Modeling Labs (CML). As a result of I’m all about sharing my exploration actions, I posted a few CML topology recordsdata on GitHub within the CML-community repository beneath Cisco DevNet.

You’ll see that one CML topology consists of simply an IOL router, whereas one other provides a Nexus 9000v swap to cowl information middle platforms as effectively. So, after you’ve learn this weblog put up, positively obtain the topologies and discover them your self.

CML topology for exploring TACACS

The best way to run a TACACS Server in Cisco Modeling Labs

Earlier than you possibly can configure TACACS on a swap or router, it’s essential to have a TACACS server out there within the community. A typical TACACS server for a manufacturing community is Cisco ISE, a full “id providers engine” for machine administration, community entry, wi-fi safety, VPN entry, and extra.

Cisco ISE is a crucial product and matter for community engineers. The truth is, we have now a certification examination devoted to it. And when you can add Cisco ISE to a CML node library utilizing the node definition out there on the CML-Group, working a full ISE server within the topology can really feel overkill when the main focus is simply on configuring TACACS for machine administration.

Fortunately, there are light-weight options. My go-to choice is the open-source “tac_plus” utility that has been out there for a few years. Tac_plus is a fundamental Linux utility that may be downloaded and put in on most Linux distributions. Whereas lively growth of the venture appears to have stalled, it really works nice and continues to be a wonderful choice for circumstances equivalent to this.

When you take a look at the picture of the CML topology, you’ll see “aaa-server” on the left-hand facet of the diagram. This can be a commonplace Ubuntu node from the CML reference platforms, with a beginning configuration setup to put in tac_plus and configure it as a fundamental TACACS server. Be at liberty to go and take a look at the configuration within the topology file for full particulars, however listed below are the fundamentals of what I did to construct my TACACS server:

  1. Set up the necessities to obtain and set up the tac_plus utility from supply code.
  2. Create the “tac_plus.conf” configuration file to specify the TACACS secret key, customers, and roles/privilege ranges for each IOS and NX-OS platforms.
  3. Create a “tac_plus.service” file to setup tac_plus as a service.
  4. Obtain, extract, set up, and begin the tac_plus server.

With the set up and configuration of the aaa-server a part of the bottom CML topology file, tac_plus shall be working and able to take requests as quickly because the lab is began.

cisco@aaa-server:~$ systemctl standing tac_plus
● tac_plus.service - tac_plus Service
     Loaded: loaded (/and many others/systemd/system/tac_plus.service; enabled; vendor pres>
     Lively: lively (working) since Mon 2024-10-14 19:16:37 UTC; 2s in the past
   Most important PID: 5982 (tac_plus)
      Duties: 1 (restrict: 2310)
     Reminiscence: 416.0K
        CPU: 2ms
     CGroup: /system.slice/tac_plus.service
             └─5982 /tacacs/sbin/tac_plus -G -C /and many others/tacacs/tac_plus.conf -d 8 >

Oct 14 19:16:37 aaa-server systemd[1]: Began tac_plus Service.
Oct 14 19:16:37 aaa-server tac_plus[5982]: Studying config
Oct 14 19:16:37 aaa-server tac_plus[5982]: Model F4.0.4.28 Initialized 1
Oct 14 19:16:37 aaa-server tac_plus[5982]: tac_plus server F4.0.4.28 beginning
Oct 14 19:16:37 aaa-server tac_plus[5982]: socket FD 4 AF 2
Oct 14 19:16:37 aaa-server tac_plus[5982]: socket FD 5 AF 10
Oct 14 19:16:37 aaa-server tac_plus[5982]: uid=0 euid=0 gid=0 egid=0 s=11063704>

The best way to allow AAA and TACACS on a Cisco IOS Router

With our TACACS server up and operational, we will now configure our IOS router to make use of it. Earlier than configuring the TACACS server on IOS, we have to guarantee some fundamental “pre-work” is completed on our router. IOS has been round for years and has skilled many modifications in how authentication and authorization are dealt with.

So, the very first thing we wish to do is make sure the “new mannequin” of AAA is enabled on our machine:

aaa new-model

Subsequent, we wish to create an area person account that may entry and administer the machine if the TACACS server turns into unreachable. You may additionally wish to use an area account for serial/console connections.

username cisco privilege 15 secret cisco

On this command, the username and password are each set to “cisco.” (Not probably the most safe selection, however that is only a lab.) The “privilege 15” a part of the command signifies that this person shall be assigned an “administrator” position. Privilege 15 is the best degree on an IOS machine and permits the person to execute any and all instructions.

We’re able to configure and take a look at TACACS now. However first, I bounce onto the console for the server and begin monitoring the logs. This manner, I can examine and confirm outcomes on the server facet in addition to on the consumer.

# On aaa-server
journalctl -fu tac_plus

# Output
Oct 14 19:16:37 aaa-server systemd[1]: Began tac_plus Service.
Oct 14 19:16:37 aaa-server tac_plus[5982]: Studying config
Oct 14 19:16:37 aaa-server tac_plus[5982]: Model F4.0.4.28 Initialized 1
Oct 14 19:16:37 aaa-server tac_plus[5982]: tac_plus server F4.0.4.28 beginning
Oct 14 19:16:37 aaa-server tac_plus[5982]: socket FD 4 AF 2
Oct 14 19:16:37 aaa-server tac_plus[5982]: socket FD 5 AF 10
Oct 14 19:16:37 aaa-server tac_plus[5982]: uid=0 euid=0 gid=0 egid=0 s=1106370448

Within the above command, the “-f” argument “follows” the log messages as they arrive in.  And the “-u tac_plus” choice limits the output to solely message from the tac_plus service.

Glorious. Now, again to the router to configure the tacacs server and add it to a bunch of servers that the router can use for AAA service.

tacacs server aaa-server
 handle ipv4 192.168.0.10
 key tacacs123

aaa group server tacacs+ AAA-TACACS
 server title aaa-server

I’m at all times a fan of testing that one thing will (or possible will) work earlier than continuing. Conveniently, IOS helps a “take a look at aaa” command that we will use.

take a look at aaa group AAA-TACACS iosadmin admin123 legacy

# Output 
Making an attempt authentication take a look at to server-group AAA-TACACS utilizing tacacs+
Consumer was efficiently authenticated.

That appears nice! And I can see the logs on “aaa-server” as effectively.

Oct 14 19:55:16 aaa-server tac_plus[6473]: join from 192.168.0.1 [192.168.0.1]
Oct 14 19:55:17 aaa-server tac_plus[6473]: login question for 'iosadmin' port unknown-port from 192.168.0.1 accepted

With a powerful sense of confidence, let’s full the AAA configuration for all three “A’s.”

! Authentication 
aaa authentication login default group AAA-TACACS native

! Authorization 
aaa authorization exec default group AAA-TACACS native 
aaa authorization console

! Accounting
aaa accounting exec default start-stop group AAA-TACACS
aaa accounting instructions 1 default start-stop group AAA-TACACS
aaa accounting instructions 15 default start-stop group AAA-TACACS

Sustaining that robust sense of confidence, let’s see if it really works. Finish/exit on the router till you might want to log again in.

ios01 con0 is now out there

Press RETURN to get began.

Consumer Entry Verification

Username:

Attempt to log into the router utilizing the TACACS credentials for the IOS machine.

Consumer Entry Verification

Username: iosadmin
Password: 

ios01#

Success! Examine the logs on the server, and you need to see one thing like this:

Oct 14 20:05:03 aaa-server tac_plus[6492]: login question for 'iosadmin' port tty0 from 192.168.0.1 accepted
Oct 14 20:05:03 aaa-server tac_plus[6493]: join from 192.168.0.1 [192.168.0.1]
Oct 14 20:05:03 aaa-server tac_plus[6493]: Begin authorization request
Oct 14 20:05:03 aaa-server tac_plus[6493]: do_author: person="iosadmin"
Oct 14 20:05:03 aaa-server tac_plus[6493]: person 'iosadmin' discovered
Oct 14 20:05:03 aaa-server tac_plus[6493]: exec authorization request for iosadmin
Oct 14 20:05:03 aaa-server tac_plus[6493]: exec is explicitly permitted by line 6
Oct 14 20:05:03 aaa-server tac_plus[6493]: nas:service=shell (handed via)
Oct 14 20:05:03 aaa-server tac_plus[6493]: nas:cmd* (handed via)
Oct 14 20:05:03 aaa-server tac_plus[6493]: nas:absent, server:priv-lvl=15 -> add priv-lvl=15 (ok)
Oct 14 20:05:03 aaa-server tac_plus[6493]: added 1 args
Oct 14 20:05:03 aaa-server tac_plus[6493]: out_args[0] = service=shell enter copy discarded
Oct 14 20:05:03 aaa-server tac_plus[6493]: out_args[1] = cmd* enter copy discarded
Oct 14 20:05:03 aaa-server tac_plus[6493]: out_args[2] = priv-lvl=15 compacted to out_args[0]
Oct 14 20:05:03 aaa-server tac_plus[6493]: 1 output args
Oct 14 20:05:03 aaa-server tac_plus[6493]: authorization question for 'iosadmin' tty0 from 192.168.0.1 accepted
Oct 14 20:05:03 aaa-server tac_plus[6494]: join from 192.168.0.1 [192.168.0.1]

I’ve coloured the server output to focus on the authentication and authorization logs individually, exhibiting that they really are two totally different phases.

However what concerning the last “A” for accounting? Press Cntr-C to cease following the service log and open up the “accounting log.”

tail -f /var/log/tac_plus.acct 

# Output 
Oct 14 20:05:03 192.168.0.1     iosadmin        tty0    async   begin   task_id=12      timezone=UTC    service=shell

It’s best to see a message just like the above exhibiting the “begin” of the session on the router. Return to the router and run “write mem” to avoid wasting the configuration modifications to reminiscence. A brand new log message ought to present up within the accounting log:

Oct 14 20:10:11 192.168.0.1     iosadmin        tty0    async   cease    task_id=13      timezone=UTC    service=shell   priv-lvl=15     cmd=write reminiscence

And now, exit the router to log off. A brand new message ought to seem as effectively:

Oct 14 20:11:02 192.168.0.1     iosadmin        tty0    async   cease    task_id=13      timezone=UTC    service=shell   disc-cause=1    disc-cause-ext=9        pre-session-time=6 elapsed_time=89  stop_time=1728936662

And BAM. All three “A’s” have been validated. Glorious work!

Hopefully, this weblog has gotten you excited to finish your personal exploration of AAA and TACACS. And, you might be in luck—the CML topology recordsdata that I discussed above (and can once more under) are there so that you can seize and use instantly. Inside them are lab guides that stroll by way of another vital AAA subjects, equivalent to utilizing native accounts on the console/serial line for IOS and configuring TACACS on Nexus units. Nonetheless, I encourage you to do some unbiased exploration and experiment with issues which can be not within the information:

What occurs if you happen to kind the flawed username/password? What occurs if the configured “tacacs key” is flawed? What occurs if the TACACS server is unreachable?

Understanding the impression of issues and failures is essential to a community engineer’s capacity to be comfy when one thing goes flawed in “actual life.” It’s a lot better to interrupt issues within the lab than await manufacturing to have points. And there’s no higher device than Cisco Modeling Labs for that exploration.

My very own AAA exploration will proceed. On this weblog and lab, I solely scratched the floor of the subject and data wanted for various certifications. RADIUS servers can be utilized as an alternative of TACACS, and what about AAA for issues like VPN authentication, community entry with 802.1x, or different platforms like ASA firewalls?

There are such a lot of extra potentialities for me to discover in later weblog posts. Would you prefer to see extra on AAA from me? Let me know within the feedback.

Till subsequent time!

Sources

 

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